Do aliens exist? I don't know the answer to that, but I certainly am open to the idea.
One of the ways that people have tried to find proof of alien life is by monitoring and analyzing radio waves from space. The problem is this - there is so much information that needs to be analyzed! If someone had millions of dollars to put in to computer systems to process data, that would be one solution. However, if you don't have the money to do so, there are other solutions. SETI@Home is one of those projects. This project started back in the late 1990's. You download a program, and it runs when you are not using your computer. You basically download the program, and your computer processes radio signals and sends the data back to the main computer. If your computer is on, this is a way to have it give back to the world.
If nothing else, your computer might find evidence of extraterrestrial life!
This is a nice example of distributed computing. Instead of one very powerful computer, you get smaller ones, and split the workload.